1. Field of the Invention
The present invention relates generally to forage harvesters and, more particularly, is concerned with apparatus and method for attaching and adjusting the positional relationship of a shearbar relative to a rotary cutterhead of the forage harvester.
2. Description of the Prior Art
In a forage harvester, typically, a header delivers crop material from the field in a generally rearward direction to feed rolls which form the crop material into a consolidated mat. The crop material mat is fed rearwardly by the feed rolls over the cutting edge on a stationary shearbar. Cutting edges on a plurality of knives peripherally arranged on a rotating cutterhead pass in close proximity to the shearbar cutting edge to chop the crop material mat into small pieces.
For maximum efficiency in the operation of the forage harvester and optimum quality of cut of the crop material, the shearbar should be positioned so that its cutting edge is as close to the passing cutting edges of the cutterhead knives as possible without ticking. Apparatus of some type is typically provided to adjust the position of the shearbar relative to the cutterhead which adjustment is generally required after each time the cutterhead knives are sharpened. Representative of the prior art are the adjustment apparatuses disclosed in deBuhr et al U.S. Pat. No. 4,190,209; Hill U.S. Pat. No. 4,295,616; Lindblom et al U.S. Pat. No. 4,436,248; Fleming U.S. Pat. No. 4,474,336; Black U.S. Pat. No. 4,506,839 and the patent application cross-referenced above.
Most desirably, for a uniformly high quality cut and to help keep the cutting edges of the knives in sharp condition, the shearbar-to-knife clearance should be constant throughout. This is difficult to achieve in practice for several reasons. One reason is that most shearbar adjustment apparatuses currently in use, such as those of the above-cited prior art, provide for adjustment of the shearbar by manipulation of components located remote from the shearbar. While providing a more convenient means for the operator to move the shearbar, the adjustment must be carried out without actually observing the shearbar-to-knife clearance. However, a procedure has evolved which alleviates much of the difficulty here. Briefly, the shearbar is moved toward the cutterhead, as the latter is turned slowly, until the knives thereon tick the shearbar lightly. When the knives begin to tick, the shearbar is then backed off from the cutterhead until the ticking stops.
The second reason for shearbar adjustment difficulty relates to the way in which the shearbar is commonly supported in the forage harvester. To explain, the shearbar is typically seated and fastened on a support member in such a way that the shearbar will be capable of withstanding the forces encountered during the chopping operation without backing away from the cutterhead. The approach is to ensure that a degree of contact is maintained between the shearbar and the support member along the entire length of the shearbar that is sufficient to create frictional forces therealong capable of countering the chopping force.
One known way to provide such degree of contact of the shearbar with the support member is to configure the support member with a convex or crowned upper surface. When the shearbar is then fastened to the support member, the shearbar becomes clamped against the support member and actually bows or bends slightly into an arched shape in seating over the crowned top surface of the support member and thereby provides good contact over the entire length of the shearbar. However, it has been found that, due to the bending, the shearbar-to-cutterhead clearance varies significantly, being less at the middle of the shearbar than at its opposite ends, along the length of the shearbar. This results in reduction of the uniformity of cut and, frequently, of the harvester cutting efficiency.
The above-cited Black patent attempts to overcome the aforementioned negative side effects associated with purposely bending the shearbar in fastening it to the crowned support member by machining a concavity in the cutterhead-facing shearbar surface. The concavity is designed to compensate for the effect of the convexity of the upper shearbar surface by placing the opposite portions of the cutting edge defined by the intersection of the two nonplanar surfaces closer to the cutterhead and thereby positioning the overall nonlinear cutting edge at a more uniform clearance from the cutterhead.
However, the solution of the Black patent appears to have certain significant shortcomings. First, it will surely increase the cost of fabricating the shearbar since machining the concavity introduces additional costly manufacturing steps. Second, the benefits of a permanent concavity will only be realized over an initial short portion of the ordinary useful life of the shearbar. The preformed concavity only reduces the clearance problem initially. Once normal wear to the shearbar distorts the original configuration of the concavity, it can no longer provide the means by which the shearbar can be adjusted to a uniform clearance with the cutterhead.
An optimum solution for resolving the difficulty of adjusting the shearbar to a uniform clearance from the cutterhead does not appear to reside in any of the adjustment apparatuses of the above-cited prior art. Consequently, a need still exists for a different approach to resolving of this difficulty.